325 MHz / 1



325 MHz / 1.3 GHz Frequency Converter Module for Vertical Cavity Test Stand

Bob Webber

10/26/2007

Introduction

Plans are being developed to test 325 MHz superconducting spoke cavities in the Fermilab ILC Vertical Test Stand (VTS) in Industrial Building #1. It is prudent to fit the 325 MHz activity into the normal VTS 1.3 GHz operations as seamlessly as possible to take advantage of the existing VTS control system test and data acquisition applications. This can be accomplished through an electrical interface that converts just four RF signals between the two frequencies. This note describes the 325/1300 MHz frequency converter module designed for that purpose.

Signals

The four RF signals that must be interfaced between the 1.3 GHz operating frequency of the existing VTS system and the 325 MHz resonant frequency of the spoke cavities are:

• Low level RF drive signal to the amplifier powering the cavity

• Cavity incident power signal (forward power)

• Cavity reflected power signal (reverse power)

• Cavity transmitted power signal (cavity field probe)

The RF drive signal must be down-converted from 1.3 GHz to 325 MHz; the other three signals must be up-converted from 325 MHz to 1.3 GHz.

The VTS LLRF System and Signal Levels

The VTS low level RF and data acquisition system is described in “Functional Description of the ILCTA-IB1 Cavity Test Stand RF, Control, and DAQ System” by J. Ozelis (Fermilab) and T. Powers (TJNAF) dated June 5, 2007. The RF circuits for this VTS system offer “a few hundred MHz bandwidth” for locking to the resonant frequency of the cavity under test; this is more than adequate to cover the expected ( ................
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